Luminol Demo

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Oxidation of Luminol


Equipment

  • 3 1L plastic Nalgene bottles (one for each solution and a third for waste)
  • 2 small beakers (~100 mL)
  • 1 large beaker or Erlenmeyer flask (~500 mL)
  • Ring stand
  • Clamp
  • Spiral tubing
  • Funnel
  • Gloves
  • Safety Glasses

Recipe

Solution A:

  • 4.0 g anhydrous sodium carbonate, Na2CO3
  • 24.0 g sodium bicarbonate, NaHCO3
  • 0.2 g luminol (3-aminophthalhydrazide)
  • 0.4 g copper(II) sulfate pentahydrate, CuSO4.5H2O
Dissolve all these in ~250 mL water and dilute to 1L. Should be a clear blue liquid.

Solution B:

  • 50 mL 3% hydrogen peroxide, H2O2 (drug store strength)
Dilute to 1L to make a 0.15% solution.

Demo


Connect the funnel to one end of the spiral hose, and clamp this into the ring stand. Have the other end drain into the large beaker. Be sure to have the lights off and all window blinds closed for the demo. Pour equal parts solutions A and B into the funnel and watch it glow!

Note: You can substitute a spiral-shaped condenser, like those from a Soxhlet extraction apparatus, for a spiral tube. You may still need a small length of tygon tubing to connect the funnel to the condenser.

The Reaction


  • Sodium carbonate and sodium bicarbonate act as a base, to convert the dissolved luminol into its dianion.
luminol_1.gif
  • Copper ions act as a catalyst, with hydrogen peroxide to decompose it into water and oxygen.
luminol_2.gif

  • Luminol reacts with oxygen, to form a new molecule in an excited state.
luminol_3.gif
  • The excited state molecule relaxes to the ground state, giving off blue light.
luminol_4.gif

Other Demo Ideas


  • Make a solution of luminol, bicarbonate, and carbonate, but without the copper. Mix with peroxide solution and place in a beaker. Sprinkle various metal salts into the solution and see if it glows. (I haven't tried this, so it may or may not work.)